Rotor Axis Research Articles

Secondary surge phenomenon of the compressor during surge recovery and its mechanism analysis

This paper explores the secondary surge during compressor surge recovery. Utilizing the test rig at Northwestern Polytechnical University, the surge is induced by tail cone adjustment. A secondary surge follows tail cone retraction post-initial surge. Signal changes are analyzed, and causes are expounded from energy and fluid dynamics. Experimental outcomes confirm the secondary surge is repeatable and observable under set conditions. Its frequency stabilizes at 4.83 Hz across consecutive events and rotor axes, being system-inherent. From energy, with enthalpy as a proxy, potential energy amasses as the compressor interacts with cavity potential shifts from tail cone changes. Exceeding kinetic supply instigates violent airflow oscillations. Peak pressure trends and simulations suggest surge likelihood at ∼3.33 × 105 J enthalpy. In fluid dynamics, post-initial surge, a stall state ensues. Tip clearance vortices from spillage and backflow expand, merge, and fill the passage. Their pre-secondary surge breakdown elevates pipeline pressure, causing gas reflux and surge recurrence. Conclusively, this research enhances compressor secondary surge comprehension, offering support for design optimization and anti-surge strategies.

An Identification Method for Rotor Axis Orbits based on Enhanced Hierarchical Multivariate Fuzzy Entropy and Extreme Learning Machine

An Identification Method for Rotor Axis Orbits based on Enhanced Hierarchical Multivariate Fuzzy Entropy and Extreme Learning Machine

Method for vibration suppression in rotary machines using multiple automatic ball balancers

An automatic ball balancer (ABB) is a device that is used to automatically balance an eccentric rotor; these are typically used in rotary machines with unknown or variable imbalances. The typical construction of an ABB consists of several balls in a ring race. The balls can move freely inside the race, which changes the eccentricity radius and phase angles relative to the rotor. The automatic balancing process requires an ABB unit to be installed on an eccentric rotor's axis; thus, its application is quite limited and usually requires the redesign of a rotary machine. This paper presents a new method for eliminating vibrations in rotary machines by using multiple ABBs that are mounted away from the rotor's axis. In this application, ABBs can be considered to be unbalanced rotary masses with adjustable eccentricity radii and phases. Theoretically, this ability allows for the total reduction of the inertial force from an eccentric rotor; however, the parameters of the ABBs must be set correctly. The process of setting the eccentricity radius and phase in each ABB occurs due to a self-synchronization phenomenon and generally depends on the physical parameters of either a rotary machine or ABBs. Both analytical and numerical investigations that were based on the mathematical model of a system of a rotary machine with a pair of ABBs allowed us to formulate basic rules to apply such a system in existing rotary machines without interference on the rotors.

A Prediction Model of Two-Sided Unbalance in the Multi-Stage Assembled Rotor of an Aero Engine

In rotating machinery with a multi-stage assembled rotor, such as is found in aero engines, any unbalance present will undergo unknown changes at each stage when rotating the assembly phases of the rotor. Repeated disassembly and adjustments are often required to meet the rotor’s residual unbalance specifications. Therefore, developing a prediction model of this two-sided unbalance for a multi-stage assembled rotor is crucial for improving the first-time assembly pass rate and assembly efficiency. In this paper, we propose a prediction model of the two-sided unbalance seen in the multi-stage assembled rotor of an aero engine. Firstly, a method was proposed to unify the mass feature parameters of each stage’s rotor into a geometric measurement coordinate system, achieving the synchronous transmission of geometric and mass feature parameters during the assembly process of the multi-stage rotor. Building upon this, a linear parameter equation of the actual rotation axis of the multi-stage rotor was established. Based on this axis, the mass eccentricity errors of the rotor were calculated at each stage, further enabling the accurate prediction of two-sided unbalance and its action phase in a multi-stage rotor. The experimental results indicate that the maximum prediction errors of the two-sided unbalance and its action phase for a four-stage rotor are 9.6% and 2.5%, respectively, when using this model, which is a reduction of 53.0% and 38.1% compared to the existing model.

Synchronised WindScanner field measurements of the induction zone between two closely spaced wind turbines

Abstract. Field measurements of the flow interaction between the near wake of an upstream wind turbine and the induction zone of a downstream turbine are scarce. Measuring and characterising these flow features in wind farms under various operational states can be used to evaluate numerical flow models and design of control systems. In this paper, we present induction zone measurements of a utility-scale 3.5 MW turbine with a rotor diameter of 126 m in a two-turbine wind farm operating under waked and unwaked conditions. The measurements were acquired by two synchronised continuous-wave WindScanner lidars that could resolve longitudinal and lateral velocities by dual-Doppler reconstruction. An error analysis was performed to quantify the uncertainty in measuring complex flow situations with two WindScanners. This is done by performing a large-eddy simulation while using the same measurement layout, modelling the WindScanner sensing characteristics and simulating similar inflow conditions observed in the field. The flow evolution in the induction zone of the downstream turbine was characterised by performing horizontal-plane dual-Doppler scans at hub height. The measurements were conducted for undisturbed, fully waked and partially waked flows. Evaluation of the engineering models of the undisturbed induction zone showed good agreement along the rotor axis. In the full-wake case, the measurements indicated a deceleration of the upstream turbine wake due to the downstream turbine induction zone as a result of the very short turbine spacing. During a wake steering experiment, the interaction between the laterally deflected wake of the upstream turbine and the induction zone of the downstream turbine could be measured for the first time in the field. Additionally, the analyses highlight the affiliated challenges while conducting field measurements with synchronised lidars.

Aerodynamic Performance of a Hovering Cycloidal Rotor: A CFD Study with Experimental Validation

A three‐dimensional (3D) unsteady Reynolds averaged Navier‐Stokes (URANS) computational fluid dynamics (CFD) toolkit for cycloidal rotors was developed and used to perform a parametric study. It included blade aspect ratio, side disks, pitch mechanism, blade camber, and shaft size. The influence of the pitch rod length showed the importance of the lift distribution between the upstream and downstream parts of the rotor cylinder. The application of blade camber significantly affected thrust and power, while having a limited effect on efficiency. A similar effect was obtained by varying the pitch rod lengths. The presence of a central axis in the rotor had a negligible effect on efficiency. The most significant impact on efficiency came from the side disks, which behaved similarly to winglets on fixed‐wing aircraft. However, changing the aspect ratio of the blades showed a similar response to that of aircraft wings, but with a smaller effect, making it conceivable to fly a square-bladed cyclorotor without side disks. To verify the CFD model, a cycloidal rotor was also built using 3D printed parts and carbon fiber tubing. It was then operated on a test rig where thrust and power were measured for speeds ranging from 408 to 2528 RPM. On the test bench, the blades were pitched with a uniform asymmetric mechanism. The maximum nose‐up pitch angle in upstream of the rotor axis was 34.8°. Due to its rotation around the rotor and its pitching in the opposite direction, the maximum nose‐up pitch angle of the downstream blade was 38.6°. The obtained rotor thrust and power curves and the flow visualization around the rotor confirmed the validity of the CFD toolkit.

Modeling and dynamic characteristics analysis of bearing pedestal early looseness in dual-rotor system

In order to study the dynamics in a dual-rotor system in the presence of a bearing pedestal early looseness fault, a 12-degree-of-freedom dual-rotor system bearing pedestal looseness fault dynamic model considering gyroscopic moments is developed. The Newmark-β method is used to solve the developed model. The dynamic response characteristics of the dual-rotor system when the bearing pedestal is loosened are analyzed. A dual-rotor fault simulation test bench is built to carry out bearing pedestal looseness fault simulation experiments. The comparative results show that the fault frequency distribution pattern in the simulation analysis envelope spectrum is consistent with the experimental results, which proves the validity of the proposed dynamics model. It is found that there is clippings in the rotor vibration signal when there is a bearing pedestal early looseness fault in the dual-rotor system. In the envelope spectrum there are high and low pressure rotor rotation frequency, the sum of frequencies and 2-fold the characteristic frequency of rotor rotation frequency. With the increase of rotational speed ratio, the amplitude of envelope spectrum characteristic frequency increases. When the bearing pedestal is loose, the loose rotor axis trajectory is elliptical-like, and the rotor axis trajectory has a tendency to be more chaotic. Capturing the vibration signal characteristics of a dual-rotor system at very small loosening angles is necessary for preventing larger looseness, which is crucial for fault prediction.

Investigation of Lateral Vibrations in Turbine-generator Unit 5 of the Inga 2 Hydroelectric Power Plant

The article presents a case study on the Investigation of lateral vibrations in the turbine-generator unit 5 of the Inga 2 hydroelectric power plant in the Democratic Republic of the Congo. Lateral vibrations were experimentally determined using twelve proximity and eddy-current probes, positioned on each measurement plane. The results were analyzed using the Dasylab and R software. Hence, it was observed that the vibration amplitudes of the upper guide bearing, lower guide bearing, and pivot/rotor exceeded acceptable or critical limit values of the international vibration standard for a rotating speed between 100-250 rpm. These excesses can lead to rotor mass imbalances, the eccentricity of the rotor axis relative to the rotation axis of the shaft, and the deformation of the coupling shaft between the upper rotor shaft and the turbine rotor shaft. Subsequently, the means and the variances of the vibration amplitudes were evaluated and compared to the reference values of the international standard. The results of the compliance analysis revealed statistically significant differences between the measured amplitudes and the reference values. Thus, it indicates deviations from international specifications.

A novel three-module real-time adjustable accuracy speed estimator for active magnetic bearing system

This research aims to investigate the rotational speed estimation in active magnetic bearing (AMB) system. Rotational speed sensors are commonly employed for speed acquisition. Nevertheless, with the continuous advancement of AMB system, the inherent weaknesses of the speed sensors are becoming increasingly prominent in practical applications. Therefore, achieving online speed estimation can effectively address the engineering challenges arising from deficiencies in speed sensors. However, in terms of robustness, accuracy, and tracking performance, the existing speed estimation algorithms are insufficient to simultaneously meet the requirements of the AMB system. Moreover, present techniques are challenging to address prevalent issues in the AMB system, such as noise, harmonic interference, amplitude variations, and misalignment of the rotor axis trajectory. To tackle these problems, this work designs a novel three-module real-time adjustable accuracy speed estimator for AMB system. The algorithm employs displacement signals to estimate the rotational speed. And, it can flexibly adjust its noise resistance and accuracy through parameter tuning. Additionally, it can significantly diminish the influence of noise, harmonic interference, amplitude variations, and misalignment of the rotor axis trajectory. Finally, the simulation and experimental results demonstrate the effectiveness of this algorithm and validate its superior performance in robustness, accuracy, and tracking performance.

PROCESS ANALYSIS OF GRAIN HULLING PROCESS

Cereals are an important source of energy and contain almost all substances necessary for the normal functioning of the human body, animals and birds. The anatomical structure of the grain has an outer shell that can be removed from the surface without destroying the starch core in many technological processes. One of the ways to improve the quality of the final product is to actively treat the surface of the wheat grain to remove the husks during its preparation for grinding. For this, peeling machines of various designs, shelling machines and machines with friction rotary knives are used. The grain is processed under the influence of impact and friction pulses in the working area of the machine, with different abrasive properties of the grain surface, external frictional forces are applied to the grain from the sides of the beater, which arise when the layers are moved along the surface of the beater. Grain is used for the production of starch, molasses and alcohol, and processed grain products include flour, pasta, cereals, bread and animal feed.Cereals are characterized by the fact that they are the main source of easily digestible carbohydrates, the main energy component of food. Bread made from wheat flour weighing 500 g, and which is made from flour of the highest grade, provides about 64% of the daily need for essential acids. The quality of the final product depends significantly on the grain preparation and processing processes. Peeling machines are used as one of the main machines for this. The transport movement of grain in the machine determines the time the grain stays in the working zone, which is achieved by placing different shaped bulls at an angle to the rotor axis, equipping the working zone with races, placing the roller at an angle to the horizontal plane and changing the rotation speed. The main disadvantages of such machines are the low efficiency of the peeling process and uneven surface treatment of individual grains in the cut state.

Simulation study on rotor speed of combined rotary separator in coal pneumatic conveying

The separator is a key component of coal pneumatic conveying systems, which plays an important role in improving particle collection efficiency and reducing dust pollution. In this paper, a combined rotary separator was designed. Based on the traditional cyclone separator, the rotor blades were installed and matched with the guide vanes to increase the material separation and collection performance. The influence of rotor speed on the characteristics of the separator was studied by computational fluid dynamics simulation, and the flow field velocity and pressure distribution and the particle trajectory and separation degree were obtained. The results showed that the flow field tangential velocity plays a dominant role in the separation process and is approximately symmetrically distributed with the rotor axis as the center. The velocity of the flow field in the inner rotor is approximately positively correlated with the rotor speed, and the tangential velocity gradually decreases with the increase in the flow field height. The static pressure of the flow field is approximately axisymmetric along the rotor axis, and there is a pressure gradient from the outer separation cone to the rotor axis. The particles in the separator show a separation phenomenon based on the different sizes, and the change trend of the separation degree under different rotor speeds is similar. When the rotor speed is 160 rpm, the particles maintain the highest integrity. The rotor speed of 320 rpm has a protective effect on coarse particles above 1000 µm.

Development of a wind turbine with two multidirectional wind wheels

The object of research is a wind generator with counter-rotating blades. A special feature of this design is the presence of two wind wheels that rotate in opposite directions. Wind wheels are on the same axis, between them there is a certain distance, which is determined based on research data. The problem of modern wind power is the low range of operating wind speeds, weak generation at low wind speeds. The upper speed limit is 25 m/s, exceeding which leads to breakdowns of various units of the wind station, especially this affects the integrity of the blades, rupture of the wind wheel, cracking of the metal parts of the bearings and their fasteners. The wind turbine presented in the article allows to achieve an increase in the generation of electric energy by 50–70 %. This is achieved by increasing the relative rotational speed of the rotor relative to the stator. Therefore, even at low speeds, the rotor speed relative to the stator increases, which leads to an increase in power generation. The design of the device includes: two wind wheels, one transmits its rotation to the stator, the second to the rotor axis, a metal base, a current collector mechanism. For conducting the research, an experimental model and a semi-industrial installation were used. Results studies have confirmed the theoretical increase in the generation of electrical energy by this design. The peculiarity of the obtained results is connected with the determination of the distance between two wind wheels, the optimal distance between them corresponds to the maximum energy generation. A distinctive feature of the results obtained can be considered an increase in the number of blades on the second wind wheel

Induction Motor Vibrations Caused by Mechanical and Magnetic Rotor Eccentricity

Vibration reduction of induction motors is a significant problem that requires effective models for the effects of mechanical and electromagnetic unbalanced forces. This article presents a mathematical model of dynamics for induction motors with rotor mass eccentricity and static and dynamic magnetic eccentricity. The model allows for the influence of the gyroscopic torque of the rotor and considers the elastic-damping characteristics of each of the stator supports and their location. The model has eight degrees of freedom, which makes it possible to simulate transverse and axial vibrations of various designs’ rotors and housings of induction motors. The results of modeling the dynamics for a three-phase squirrel cage induction motor with 11 kW capacity agreed with those obtained by other authors. Simultaneously, new results were also obtained within the research. The simulation results showed that the static magnetic eccentricity causes the appearance of additional critical speed of the motor, and its value decreases in proportion to the growth of the number of pole pairs. The change of the moment of inertia of the motor at a mismatch of the main axis of symmetry of the stator and the rotor axis of rotation allowed for obtaining an actual frequency spectrum of free oscillations, including the rotational motion of the stator. Since the actual static magnetic eccentricity can additionally increase at operating frequencies due to the increase of bearing clearance caused by dynamic unbalanced load, it should be considered in the analysis of unbalanced magnetic pull. The angle of static magnetic eccentricity significantly affects the magnitude of radial vibrations. This feature should also be considered when selecting the locations of balancing weights during the rotor balancing procedure.

THREE-DEGREE-OF-FREEDOM ELECTRIC MACHINE AND ITS OPERATION MODES

This paper deals with the operating modes of a 3-degree-of-freedom (3-DOF) electric machine. The design of such a machine allows the rotor axis to rotate along two angular coordinates in a limited range of angles. This is necessary for the machine to operate as part of a small-sized, high-speed precision target detection and tracking system. Based on the 3-DOF machine dynamics model, a block diagram of a servo system has been developed for controlling the rotor motion trajectory at two coordinates. Examples are given of the implementation of rotor motion trajectories with linearly increasing Examples are given of the implementation of rotor motion trajectories with linearly increasing, as well as described by an Archimedes spiral reference signals described by an Archimedes spiral reference signals. Dependencies of the modules of the relative accuracy of rotor movement along given trajectories on the system tunings were obtained. Ref. 12, fig. 9, table. Keywords: control system, motion trajectories, three-degree-of-freedom electric machine.

Wind tunnel experimental study of aerodynamic characteristics of co-flow jet wing with built-in air source

To further investigate the aerodynamic characteristics and control mechanisms of co-flow jet wings, this study presents the design of a co-flow jet wing (CFJ-CLARKY18) with an embedded micro centrifugal compressor. The CFJ-CLARKY18 wing, based on the CLARKY18 airfoil, incorporates a miniature centrifugal compressor positioned horizontally within the wing's cavity, with its rotor axis perpendicular to the wing chord line, thus alleviating geometric constraints and the compressor's exhaust swirl. The integration of the co-flow jet device with the wing is achieved through a split-flow channel design to ensure uniform co-flow jet injection, followed by verification of jet uniformity and calibration of six jet momentum coefficients. Subsequently, static and dynamic control experiments of the co-flow jet wing are conducted in an open-return wind tunnel, utilizing force measurement systems and high-speed particle image velocimetry tools to investigate its aerodynamic characteristics and control mechanisms. Static stall tests indicate that, compared to the original wing, the CFJ-CLARKY18 wing exhibits a significant increase in lift and a noticeable delay in stall angle. At low angles of attack, an increase in co-flow jet momentum leads to a reduction in drag coefficient, with the possibility of achieving negative drag (thrust) even at high co-flow jet momentum coefficients. The results of dynamic stall tests with force measurements indicate that, while keeping the reduced frequency constant, an increase in co-flow jet momentum coefficient results in higher maximum lift and average lift coefficients, accompanied by a significant reduction in average drag coefficient and the hysteresis loop area of the lift coefficient. Despite the increased reduced frequency exacerbating the wing's stall effect, the stall effect weakens significantly once the co-flow jet momentum coefficient is increased.

Improving Savonius turbine efficiency with splitter and barrier cylinder deflector design: A Taguchi method study

Vertical axis wind turbines are wind turbines with the rotor axis perpendicular to the ground, designed to harness wind energy for electricity generation. The primary cause of low-efficiency Savonius turbines is the negative torque contribution from the returning blade. A Savonius turbine is a type of turbine characterized by its rotational direction orthogonal to the passing fluid flow and the flow interaction with advancing and returning blades, generating torque primarily through drag forces. Thus, the study proposes a novel design of a cylindrical deflector with splitters and a barrier to offset the flow field to the returning blades. This study aims to maximize the efficiency of conventional Savonius turbines using the cylindrical deflector with splitters and a barrier via a combination of computational fluid dynamics simulations and the Taguchi optimization method. The Taguchi method is used to determine the best combination of specified characteristics such as the length of the barrier (Ls/D), the barrier attachment angle (α), and the geometric shape of the cylinder deflector with a splitter and a barrier. The tip speed ratio (λ) for this study is fixed at λ = 1. The simulations and additive model revealed that the optimal combination in this study is a cylinder deflector with double wake splitters positioned at the top and middle of the deflector. The deflector is oriented parallel to the flow, and a barrier placed at the bottom of the deflector is oriented orthogonal to the flow. The optimal configuration has Ls/D ratio of 0.9 and a barrier attachment angle (α) of 10°. Therefore, the ideal combination was found to produce a power coefficient equivalent to 0.459, indicating that the performance of Savonius turbines increases by around 61% compared to previous studies.

Three-dimensional simulation of gas flow for predicting the pressure and velocity profiles inside a gas centrifuge machine using the DSMC method

In this article, using the direct simulation Monte Carlo (DSMC) method, the gas flow inside the gas centrifuge was modeled simultaneously in the Knudsen and hydrodynamic zones. So that the three-dimensional (3D) simulation of gas centrifuge in the presence of all drivers inside the rotor, including feed, scoop, baffle, etc. was done. The results showed that, the feed is an important factor in creating and intensifying the axial flow formed in the rotor axis, and choke phenomenon occurs at the point of its entry into the rotor. It was further revealed that the amount of separation power obtained from the simulation (using the DSMC method) and the experimental has a difference of 4.3%, showing the agreement of the 3D simulations with reality.

A Simple Model for Wake-Induced Aerodynamic Interaction of Wind Turbines

Wind turbine aerodynamic interactions within wind farms lead to significant energy losses. Optimizing the flow between turbines presents a promising solution to mitigate these losses. While analytical models offer a fundamental approach to understanding aerodynamic interactions, further development and refinement of these models are imperative. We propose a simplified analytical model that combines the Gaussian wake model and the cylindrical vortex induction model to evaluate the interaction between wake and induction zones in 3.5 MW wind turbines with 328 m spacing. The model’s validation is conducted using field data from a nacelle-mounted LiDAR system on the downstream turbine. The ‘Direction to Hub’ parameter facilitates a comparison between the model predictions and LiDAR measurements at distances ranging from 50 m to 300 m along the rotor axis. Overall, the results exhibit reasonable agreement in flow trends, albeit with discrepancies of up to 15° in predicting peak interactions. These deviations are attributed to the single-hat Gaussian shape of the wake model and the absence of wake expansion consideration, which can be revisited to improve model fidelity. The ‘Direction to Hub’ parameter proves valuable for model validation and LiDAR calibration, enabling a detailed flow analysis between turbines. This analytical modeling approach holds promise for enhancing wind farm efficiency by advancing our understanding of turbine interactions.

ЕЛЕКТРОМАГНІТНІ МОМЕНТИ УПРАВЛІННЯ ПРЕЦЕСІЙНИМ РУХОМ ТРИСТУПЕНЕВОЇ ЕЛЕКТРИЧНОЇ МАШИНИ

The main known structures and principles of functioning of electric machines with three degrees of freedom of rotational motion of the rotor are considered. The type of such machines in which it is possible to realize a high frequency of the rotor rotation is highlighted, which gives it the property of gyro-stabilization. The structure of the magnetic system of the machine of this type is presented and a hypothesis is put forward about the adequacy of the expressions of the classical analytical mathematical model, but the need for accurate calculation of the concentrated parameters that make up it. The distribution of magnetic flux density is analyzed based on a numerical mathematical model of a three-dimensional mag-netic field. The dependences of electromagnetic torque components and flux linkages on the rotor axis orientation and the angle of its rotation are calculated. It was concluded that the classical analytical mathematical model are adequate pro-vided that the calculating of its coefficients is based on the results of the modeling of three-dimensional magnetic field in the machine active volume and the surrounding space. It is underlined that, the amplitude of the flux linkage vector of the control winding and the fluctuations of the vector components to use in lumped parameter model must be calculated from the corresponding values of the electromagnetic torque components. Taking into account the results of the analysis of the three-dimensional field demonstrates a significant decrease in the speed of controlled precession and an increase in the amplitude of nutation. References 9, figures 10, tables 2.

Dynamic modeling and analysis of high-speed aerostatic journal bearing-rotor system with recess

To analyze the dynamic properties of high-speed aerostatic journal bearing with recess, a bidirectional fluid-structure coupling dynamic model is established. The mathematical model is established by coupling the governing equation of the transient air film flow, the flow balance equation, and the rotor motion equation. Based on the trajectory of rotor axis, trajectory of rotor center, Poincare map, time response of rotor, frequency spectrum, mass flow rate, and bifurcation diagram, the influences of operating parameters on the coupling system are analyzed theoretically and experimentally. The results indicate that the system has abundant nonlinear behavior, and the instability parameters of the system are determined. This study provides guidance for the theoretical design and practical operation of this type of system.